Ohta Hiroyuki, Miyagi Atsushi, Kato Keijiro, Fukui Kazuhiro
Department of Microbiology, Okayama University Dental School, Shikata-cho 2-chome, Okayama 700, Japan.
Microbiology (Reading). 1996 Apr;142 ( Pt 4):963-970. doi: 10.1099/00221287-142-4-963.
Actinobacillus actinomycetemcomitans, a Gram-negative periodontopathic bacterium, produces a leukotoxin belonging to the RTX family. The production of leukotoxin varies greatly among different strains of this species. In this paper the effects of growth rate and bicarbonate on the leukotoxin production by a toxin-production-variable strain (301-b) during growth in a chemostat were examined. When the bacterium was grown in anaerobic fructose-limited chemostat cultures (pH 7.0 and 37 degrees C) at dilution rates (D) ranging from 0.04 to 0.20 h-1 in the absence and presence of 10 mM bicarbonate, it produced leukotoxin as a cluster of two polypeptides (M(r) 113,000 and 120,000) and complexed with nucleic acids on the bacterial cell surface. The relationship between leukotoxin production and specific growth rate was analysed by plotting the specific rate of leukotoxin production [qLT, in microgram (mg dry wt)-1 h-1] against D. The plots were approximated to the linear relationships qLT = 2.7D-0.058 and qLT = 9.3D-0.407 without and with bicarbonate, respectively. These relationships suggest that the apparent leukotoxin production is a result of both growth-rate-dependent production and growth-rate-independent decomposition. The cellular leukotoxin level was also followed after the change from chemostat to batch culture in the same fermenter. In batch culture leukotoxin production stopped immediately and the cellular toxin level rapidly decreased, suggesting toxin decomposition. From the slopes of the approximated linear relationships between qLT and D, a theoretical maximum leukotoxin yield (YLT) was estimated as 2.7 and 9.3 micrograms (mg dry wt)-1 in the absence and presence of 10 mM bicarbonate, respectively. The increased YLT value in the cultures containing bicarbonate indicated that the addition stimulated the efficiency of leukotoxin synthesis up to about threefold. Further increases of bicarbonate concentration to between 20 and 40 mM had no effect on the total leukotoxin production, but the amount of extracellular leukotoxin increased with higher bicarbonate concentrations.
伴放线放线杆菌是一种革兰氏阴性牙周病原菌，可产生一种属于RTX家族的白细胞毒素。该菌不同菌株间白细胞毒素的产生差异很大。本文研究了生长速率和碳酸氢盐对一株产毒素可变菌株（301-b）在恒化器中生长期间白细胞毒素产生的影响。当该菌在厌氧果糖限制的恒化器培养物（pH 7.0，37℃）中，在稀释率（D）为0.04至0.20 h⁻¹的条件下，分别在不存在和存在10 mM碳酸氢盐的情况下生长时，它产生的白细胞毒素是由两种多肽（分子量分别为113,000和120,000）组成的簇，并与细菌细胞表面的核酸结合。通过绘制白细胞毒素产生的比速率[qLT，以微克（毫克干重）⁻¹ h⁻¹为单位]对D作图，分析了白细胞毒素产生与比生长速率之间的关系。在不存在和存在碳酸氢盐的情况下，这些图分别近似于线性关系qLT = 2.7D - 0.058和qLT = 9.3D - 0.407。这些关系表明，表观白细胞毒素的产生是生长速率依赖性产生和生长速率非依赖性分解共同作用的结果。在同一发酵罐中从恒化器培养转变为分批培养后，也对细胞内白细胞毒素水平进行了跟踪。在分批培养中，白细胞毒素的产生立即停止，细胞毒素水平迅速下降，表明毒素发生了分解。根据qLT与D之间近似线性关系的斜率，估计在不存在和存在10 mM碳酸氢盐的情况下，理论最大白细胞毒素产量（YLT）分别为2.7和9.3微克（毫克干重）⁻¹。含有碳酸氢盐的培养物中YLT值的增加表明，添加碳酸氢盐可将白细胞毒素合成效率提高约三倍。将碳酸氢盐浓度进一步提高到20至40 mM之间对白细胞毒素的总产量没有影响，但细胞外白细胞毒素的量随碳酸氢盐浓度的升高而增加。
